1. Field of the Invention
The present invention relates to a digital camera for an optical apparatus, suitably used in an optical apparatus such as a microscope or the like.
2. Description of the Related Art
In microscopic observation, high-quality images have been demanded to perform pathologic diagnosis based on cellular forms, and fluorescent imaging to measure changes of samples based on very weak fluorescence, etc. In place of a conventional camera system using a silver film as an imaging device, a digital camera using a solid-state imaging device (hereinafter referred to as a “CCD device”) has come to be used as means for acquiring an image.
In the CCD device, a dark current which is a very small output current flows even while light is not inputted. The dark current increases depending on increase in temperature and is added as a noise to image signals, as a result, the S/N ratio deteriorates. A method of cooling the CCD device to reduce the dark current has been adopted to improve the S/N ratio of image signals.
However, when a cooled CCD device is exposed to outer air having high humidity, dew condenses on the surface of the CCD device and moisture sticks to the surface. This degrades images or cause operational errors in peripheral devices. A sealed configuration has been adopted to avoid this problem. In the sealed configuration, the CCD device is configured in a sealed container having low humidity.
The following technique is known as a conventional sealed configuration (see Jpn. Pat. Appln. KOKAI Publication No. 6-45570).
Specifically, the sealed configuration is configured as follows. A cable, which has no air-permeability and uses a thin film material, is extended to the outside from between two halves into which one sealed container is divided. O-rings are inserted between the cable and the halves to fill gaps and to seal them.
However, in the sealed configuration described above, a special cable must be manufactured. This makes the cable expensive and difficult to acquire a large current capacity.
The CCD device described above also comprises light-receiving devices arrayed two-dimensionally. Resolution depends on the total number of light-receiving devices. If the CCD device is divided into a large number of devices to improve the resolution, however, sensitivity deteriorates and the apparatus becomes more expensive.
A means for acquiring an image signal with high image quality from a CCD device has already been disclosed (see Jpn. Pat. Appln. KOKAI Publication No. 9-219867). This is a technique which increases the number of pixels by moving two-dimensionally one CCD device having a small number of pixels, without degrading sensitivity.
In the technique described above, a plate-like metal member is bent, and a CCD device is assembled in a displacement mechanism using elastic force of the bent member. Further, improvements in number of pixels are achieved by moving two-dimensionally the CCD device by means of the displacement mechanism, without degrading sensitivity.
However, in this means for achieving high image quality of the CCD device, means for reducing the dark current of the CCD device is not proposed.
As has been described above, in the sealed configuration of a conventional CCD device, suffers it is necessary to manufacture the special cables and the substrate configuration is limited due to the current capacity. In addition, the conventional means for achieving high image quality of the CCD device can improve the resolution but increases the dark current, which causes deterioration of the S/N ratio.